Proton transfer reactions of N-aryl triazolium salts: unusual ortho-substituent effects

Previous studies of the C(3)-hydrogen/deuterium exchange reactions of the triazolium ion conjugate acids of triazolyl N-heterocyclic carbenes revealed a change of mechanism under acidic conditions with N1-protonation to a dicationic salt. Interestingly, the data suggested an increase in pKaN1 in the presence of a N-pentafluorophenyl substituent relative to other N-aryl substituents with hydrogens or methyl substituents rather than fluorines at the ortho-positions. To probe the presence of an apparent donor effect of a N-pentafluorophenyl substituent, which differs from the more common electron withdrawing effect of this group, we have studied the analogous deuterium exchange reactions of four triazolium salts with heteroatoms or heteroatom substituents in the 2-position and/or 6-position of the N-aryl ring. These include triazolium salts with N-2,4,6-tribromophenyl 11, N-2,6-dichlorophenyl 12, N-2-pyridyl 13 and N-2-pyrimidinyl 14 substituents. The log kex – pD profiles for 11, 12 and 14 were found to show similar trends at lower pDs as for the previously studied N-pentafluorophenyl triazolium salt, hence supporting the presence an apparent donor effect on pKaN1. Surprisingly, the log kex – pD profile for N-pyridyl salt 13 uniquely showed acid catalysis at lower pDs. We propose herein that this data is best explained by invoking an intramolecular general base role for the N-(2-pyridyl) substituent in conjunction with N1-protonation on the triazolium ring. Finally, the second order rate constants for deuteroxide ion catalysed C(3)-H/D exchange (kDO, M−1 s−1), which could be obtained from data at pDs >1.5, were used to provide estimates of C(3)-carbon acid pKaC3 values for the four triazolium salts 11, 12, 13, 14

Characterisation of LCF performance of X100 weld-joints: Mechanistic yield strength modelling, finite element analyses and DIC testing

This paper is concerned with the effect of welding on the fatigue behaviour of X100 material for steel catenary risers. The methodology includes both modelling and experimental characterisation. The modelling combines (i) a physically-based yield strength model to capture the thermally-induced microstructural heterogeneity and associated spatial variations in relative contributions of the key strengthening mechanisms due to welding, and (ii) a five-material cyclic plasticity model with a Coffin-Manson strain-life fatigue model for prediction of cross-weld heterogeneity in cyclic plasticity and fatigue response. The combined non-linear isotropic-kinematic cyclic plasticity behaviour of the five weld joint constituent materials (PM, weld metal (WM) and heat-affected zone (HAZ) subregions) is implemented via a user material (UMAT) subroutine, including Kocks-Mecking monotonic-cyclic evolution of yield stress. The experimental methodology consists of tensile tests with digital image correlation (DIC) for X100 PM and cross-weld samples. The results indicate that the primary phenomenon driving the detrimental effect of welding on fatigue is the evolution of cyclic strain localisation in the inter-critical heat-affected zone (ICHAZ), leading to predicted ICHAZ failure

Placental growth factor in assessment of women with suspected pre-eclampsia to reduce maternal morbidity: a stepped wedge cluster randomised control trial (PARROT Ireland)

To determine whether the addition of placental growth factor (PlGF) measurement to current clinical assessment of women with suspected pre-eclampsia before 37 weeks’ gestation would reduce maternal morbidity without increasing neonatal morbidity